As is well known, in subtractive color photographic processes, an oxidation product of an aromatic primary amine type color developing agent, produced by reduction of exposed silver halide grains with the color developing agent, is oxidatively coupled with yellow, cyan, and magenta dye-forming couplers in silver halide emulsions to form color images.
In this process, active methylene group-containing compounds are generally used as yellow couplers for forming yellow dye (i.e., "yellow couplers", etc., as used herein refers to yellow-dye-forming couplers, etc.); pyrazolone type, pyrazolobenzimidazole type, or indazolone type compounds are used as magenta couplers for forming magenta dyes; and phenolic or naphtholic type compounds are used as cyan couplers for forming cyan dyes.
Typically, each coupler is added to a silver halide emulsion as a solution thereof dissolved in a high-boiling organic solvent which is substantially insoluble in water together, if necessary, with an auxiliary solvent, or as an alkaline aqueous solution thereof. In general, the former method provides better light fastness, humidity resistance, heat resistance, graininess, and color sharpness than the latter.
Each coupler should not only merely form a dye, but should also have a large solubility in a high-boiling organic solvent or an alkali and a good dispersibility and stability in a silver halide photographic emulsion, to form a dye with good fastness to light, heat, and humidity, to possess excellent spectral absorption characteristics and good transparency, and to form a distinct image with, as is more important, high color density and large dye-forming rate.
Furthermore, it has become economically necessary to avoid use of benzyl alcohol, conventionally added upon color development processing, for the purpose of reducing the cost for processing waste liquor. However, under the present techniques, in general, the use of a benzyl alcohol-free color developing solution deteriorates coloration properties of couplers added to silver halide photographic emulsions, that is, it decelerates the dye-forming rate and reduces maximum color density. Therefore, it has been desired to develop yellow couplers whose coloration properties do not depend upon benzyl alcohol and which form images with improved preservability. Conventionally known yellow couplers are generally so dependent upon pH as to coloration properties that extremely strict and careful control of pH has been required during color development processing. However, optimal pH of color development usually varies somewhat depending upon individual color developing agents, couplers, or the combination of couplers. Thus, yellow couplers whose coloration properties are less pH-dependent are required. Yellow couplers fully satisfying the above-described requirements have not yet been found, however.
Conventionally known yellow couplers are as follows. For example, U.S. Pat. No. 3,408,194 describes yellow couplers which have a sulfamoyl group in the 4-position of .alpha.-pivaloylacetanilide and in which one hydrogen atom in the active site is substituted by an aryloxy group. These couplers form dyes with poor preservability and imperfect spectral absorption characteristics, and thus are not satisfactory.
Japanese Patent Application (OPI) No. 87650/75 describes yellow couplers which possess an alkylsulfonamido bond, an aralkylsulfonamido bond, a benzenesulfonamido bond, an alkoxybenzenesulfonamido bond or an arylsulfonamido bond in the 5-position of .alpha.-pivaloylacetanilide, and in which one hydrogen atom in the active site is substituted by an aryloxy group (the term "OPI" as used herein refers to a "published unexamined Japanese patent application"). Some of these couplers are not substantially responsive to pH-change of developer as to coupling reactivity, but they form dyes with poor preservability and generally show unsatisfactory coupling reactivity in a benzyl alcohol-free color development processing solution.
Japanese Patent Application (OPI) Nos. 115219/77 and 48541/79 describe yellow couplers which have an alkylsulfonamido bond or a phenoxyalkylsulfonamido bond in the 5-position of .alpha.-acylacetanilide and in which a heterocyclic ring is bound to the active site via the nitrogen atom of the heterocyclic ring. These couplers do not show sufficient coloration properties in color development processing not using benzyl alcohol.
Japanese Patent Application (OPI) No. 142340/80 describes couplers which have an alkoxyalkylsulfonamido group in the 3-position of .alpha.-acylacetanilide. These couplers have an ether bond in the hydrophobic alkyl moiety of the alkylsulfonamido group to increase hydrophilicity, and, as a result, increase coupling activity of the couplers. However, they still do not completely satisfy the requirements described hereinbefore.